Elastic thread-cutting die with automatic adjustment



July 16, 1957 N. PER LAKI 2,799,028

ELASTIC THREAD-CUTTING DIE WITH AUTOMATIC ADJUSTMENT Filed March 12,1954' 3 Sheets-Sheet l y 1957 N. PERLAKI 2,799,028

ELASTIC THREAD-CUTTING DIE WITH AUTOMATIC ADJUSTMENT Filed March 12,1954 3 Sheets-Sheet 2 Fig. 6

hp 7 INVENIOR N. PERLAKI July 16, 1957 ELASTIC THREAD-CUTTING DIE WITHAUTOMATIC ADJUSTMENT 3 Sheets-Sheet 3 Filed March 12, 1954 United StatesPatent ELASTIC THREAD-CUTTING DIE WITH AUTOMATIC ADJUSTMENT NandorPerlaki, Budapest, Hungary, assignor to Licencia TalalmanyokatErtekesito Vallalat, Budapest, Hungary, a firm Application March 12,1954, Serial No. 415,730

Claims priority, application Hungary March 16, 1953 Claims. (Cl. 10111)This invention relates to thread-cutting dies for machining materialsand adapted to work with a clearance angle.

Various constructions of thread-cutting dies have hitherto beensuggested, their common characteristic feature being stiffness orrigidity during operation in order to ensure the exact size .of thethread to'becut.

The most usual p of Such dies haSQdiSK-HKQShaPB 1 known construction thebasic idea is to possibly eliminate with radially arrangededge-supporting members or. cutting lips. Its significance lies inrelatively low manufacturing costs and in the possibility of bilateraluse. However, in order to permit such bilateral use they have cuttingedges when removed from the work-piece. More said drawbacks of the knownthread-cutting dies.

over, they are rather sensitive as to the manufacture of the chuckinaccuracies of which entail an uneven load distribution of the cuttinglips.

The present invention aims at eliminating the ab loge e invention isbased upon the discovery that'in contradist'inction to the hithertoknown thread-cutting dies with which rigidity or stiffness in operationwas a predominant principle of construction-simple manufacture, goodcutting qualities and a long life-time can be obtained if thethread-cutting die as a whole is rendered freely and the drawback that aclearance angle may only be formed with the initial profiles of theircutting edges. The rest of the profiles used for calibrating thethreadshaving no clearance angle, the whole of the threaded surface ofthe cutting lips is exposed, even during removal of the die from thework piece, to the wearing effect of the cut material. A considerableadditional turning moment is required thereby resulting in anundesirable friction heat. In consequence hereof the working dimensionsof the dies rapidly increase and, at the same time, theMorethread-cutting edges become prematurely dull. over, the lack ofclearance angle has the further drawback that' the cutting process isaccompanied by a displacement of the material to be machined whereby thewear of the cutting edges is additionally increased and their profilesrendered distorted. Neither the increase of the working diameter nor thedistortion of the profiles can be eliminated by re-sharpening' the dieas is known to those skilled in the art. Another important drawback ofsuch thread-cutting dies consists in that the cutting edges, because'ofthe rigid construction of the 'die, are liable to split off whenremoving the die from the work piece. I

For sake of more favourable cutting conditions it has been suggested toprovide even the calibrating cutting edges with a suitable clearanceangle either by grinding or by a predetermined permanent deformationofthe cutting lips. This is, however, possible only on expenses of thebilateral use whereby the life-time of the dies is considerablydecreased. Apart therefrom, the rate of alteration of the workingdiameter of the die when resharpened as well as its liability as tosplitting off of the cutting edges as, to a minor degree, is the casewith the previously described dies with no clearance angle, is evenincreased by the presence of suchan angle. More: over, re-sharpening isrelatively more frequently needed since the cutting edges are exposed toan increased wear when removing the die from the work piece.

In order to meet the double requirement as to provid' ing a clearanceangle by means of deformation previous to operation of the die andpermitting bilateral use thereof it has been proposed to partly give upthe principle of rigidity insofar the dies are, by means of radial slotsin the cutting lips,- rendered elastically deformable. The needed valueof the clearance angle is then obtained by "a suitable predeterminedelastic deformation of the cut elastically deformable in operationrather than stiff or rigid. Thus, the new thread-cutting die forms aclosed elastic framework selected for elastic deformation under theaction of the forces of cutting Whereas with the the deforming effect ofthe cutting forces on the die proper. The aforesaid free andpremeditated deformation of the die is then made use of to constitutethe desired clearance angle. Accordingly, the improved thread-cut;- tingdie "for machining materials and. adapted to work with a clearanceangle, having cutting ,edges and support members for supporting thecutting edgesin the usual manner, comprisesin compliancewith themainfeature of the present inventione1astically deformable girder membersconnecting the support members to one another so as to form a closedelastic system, this system being selected so that the needed value ofthe clearance angle will, by elastic deformation of the girder members,automatically be obtained upon machining engagement of the cutting edgeswith a material to be. machined.

' Other features and objects of the present invention will be understoodby the following description and. claims reference being taken to theaccompanying drawings in which:

Fig. 1 shows, by way of example, the perspective view of an embodimentof the invention.

I Fig. 2 represents the front View of the thread-cutting die accordingto Fig. 1 in both its inoperative and operative positions. 7

Fig. 3 illustrates, 'likewisely by way of example, the front view ofanother preferable embodiment of the invention in its inoperativeposition.

Fig. 4 is a like view showing the thread-cutting die according to Fig. 3in its operative position.

Figs. 5 to 7 illustrate, on a relativelysmaller scale, a preferablemethod of manufacturing the bulk of the thread-cutting die according toFigs. 3 and 4 by plastically shaping tubular material. Finally:

Fig. 8 represents the perspective view of theembodiment shown in Figs. 3and 4 clamped in a chuck in its operative position. Same referencecharacters throughout the drawings.

Referring to Figs. 1 and 2, the thread-cutting die represented isprovided with cutting edges 10 and support members or cutting lips 11for supponting the cutting edges 10. The support members 11 are-incompliance with themain feature of the inventionconnected to one anotherby elastically deformable girder members 12 so as to form a closedelastic system. The system is selected so that the needed value of theclearance angle will, by elastic deformation of the girder members 12,automatically be" obtained upon machining engagement of the designatelike details cutting edges 10 with a material to be machined as willclosure the support members 11 or web portion of the thread-cutting diedo not take part individually in the elastic deformation of thecircuitous ring shaped body formed by the combination of members 19, 11,12. Deformation whatever of the cutting edges are obviously to beavoided which means that the support members 11 supporting the cuttingedges 16 must not be deformed whenever a deformation of the system as awhole takes place.

With the represented embodiment, the support members 11 and the girdermembers 12 are symmetrically arranged with respect to an axialcentre-line 13 which is also the axis of rotation of a work piece 14 tobe machined by the thread-cutting die. The advantage of such anarrangement consists in that the system 1%), 11, 12 is uniformlydeformable around the axis 13, that is a certain deformation of one ofthe girder members 12 entails a like deformation of the rest of suchmembers. Thus, the load of the cutting edges 10 is evenly distributedthroughout the thread-cutting die when being in machining engagementwith the work piece 14. Furthermore, the uniform deformation of thegirder members 12 has, as will be seen, its special significance whenadjusting the thread-cutting die within a chuck receiving the same.

Moreover, with the represented embodiment the threadcutting die is builtup of three congruent parts each comprising a cutting edge 10, a supportmember 11 and a girder member 12. Such an arrangement has itssignificance in that the thread-cutting die is adapted to be centered bysupporting at three points. The system 10, 11, 12 proper beingelastically deformable, the cutting edges 10 will then in all casesoccupy a concentric position with respect to the axis 13 of rotation ofthe work piece 14 and evenly participate in the load notwithstandingwhether the congruancy of the parts of the system 10, 11, 12 is lessthan perfect or the work piece 14 is not quite rectilinear.

It is noted that the initial pro-files of the cutting edges 10 areshaped so as to form a conical entrance and may have a permanentclearance angle as is well known to those skilled in the art and,therefore, not represented in the drawings.

In Fig. 2, the inoperative position of the die is represented by solidlines whereas the operative position thereof is illustrated bydot-and-dash lines. The free elastic deformation of the die is renderedpossible by bracket means 15 engaging the die each between two adjacentgirder members 12 and bearing with their front surfaces against the dieopposite to the supporting members 11. The dimensions are selected so asto permit rolling of the support members 11 around the axis 16 of thecylindrically shaped bearing surfaces of the bracket means 15.

In operation, when the work piece 14 is rotated in the direction of thearrow 17, the cutting edges 10 get into machining engagement with thematerial to be machined, i. e. the work piece 14. In consequence hereof,the system 10, 11, 12 becomes elastically deformed as indicated by thedot-and-dash lines so that the radial centre-lines 18 of the supportmembers 11 rotate by an angle on around the axis 16 into a position 18'whereby a clearance angle a appears behind each of the cutting edges 10the profile of which has to be selected in consideration of this slightrotation as will be obvious to those skilled in the art. The angles aare of the same degree value.

It is clear from the drawing that the cutting edges 10 by rotatingaround the axis 16 approach the axis 13. Thus, the working radius 19 ofthe die is less than its radius 20 associated with the inoperativeposition thereof. Upon removing the die from the work piece 14 themachining engagement between the cutting edges 10 and the work piece 14is automatically relieved since the die then regains, by means of itselasticity, the inoperative position thereof illustrated by solid lines.Thus, during removal of the die, the cutting edges 10 do not contactwith and are not exposed to wear on the threads cut on the work piece14. Obviously, the possibility of their splitting off is likewiselyavoided thereby.

With the embodiment shown in Figs. 3 and 4 the cutting edges 10, thesupport members 11 and the girder members 12 are formed so as to besymmetrical not only with respect to an axial centre-line, viz. to theaxis 13 of rotation of the work piece 14 but also relatively to radialcentrelines going through the support members 11, i. e. to thecentre-lines 18 of the latter. The main significance of such anarrangement consists in the possibility of using the die bilaterallysince, in this case, the system 10, 11, 12 is uniformly deformable inboth directions around the axis 13. Moreover, the cutting edges 10 beingof circular shape with respect to the axis 13, they require but lowcosts of manufacture and yet receive a suitable clearance angle inoperation. Furthermore, the die retains its working radius 19 as well asthe profile of its cutting edges 10 within the limits of the standardtolerances during the whole period of its life-time even if re-shaped aswill be clear to those skilled in the art. It is likewisely importantthat such improved dies are feasible even in case of the smalleststandardised working diameters 19.

Otherwise, the represented embodiment differs from the previouslydescribed one insofar that the cutting edges 10 are formed by bits 21fixed by fastening means, e. g. solderings 22, to the support members 11as is well known to those skilled in the art and, therefore, notdescribed in closer details.

Obviously, the support members 11 might be formed interchangeable, forinstance by means of dove-tailed connections between the support members11 and the girder members 12. However, it is preferable to form theelastically deformable girder members 12 integral with the supportmembers 11 and, mainly in case of small dimensions, with the cuttingedges 1% as well. If the system is partly or wholly integral, asdescribed above, the bulk of the thread-cutting die comprising at leastthe support members 11 and the girder members 12 will preferablybe madeof tubular material plastically shaped to the desired profile of thesystem.

One method of manufacturing the die by the aforesaid plastic shapingconsists in drawing a tube of suitable material and dimensions in anumber of steps to a predetermined final shape of cross section. Themain steps of such a process are shown, by way of example, in Figs. 5 to7 of the drawings. Fig. 5 illustrates a cross section 23 of the tubeselected as the starting material of the process. Fig. 6 illustrates anintermediate cross section 24. The tubular body of this cross section isalready suitable for being drawn, by means of plastically shaping thestraightlined sections of the profile 24, to the final profile 25 shownin Fig. 7. The microstructure of the bulk of the die examined in a crosssection like the profile 25 will obviously show the nature of themanufacturing process by a series of continuous lines following thecurves of the support members 11 and the girder members 12.

Another process of plastically shaping tubular materials to the desiredprofile of the system substantially consists in extruding a tubular bodythrough a die provided with a caliber e. g. of the form shown in Fig. 7as, otherwise, is well known in the art and, therefore, not discussedhere in closer details. Also in this case the nature of themanufacturing process is recognisable by examination of themicrostru-cture of the die in-an e. g. axial section sinceinhomogenities of the material will show a sort of symmetry across thewidth of the bulk, in contradistinction to cases Where the bulk of thedie has, by means of cutting operations, been worked out as a whole froma solid body.

Referring to Fig. 8, the system 10, 11, 12 is surrounded by a chuckmeans 26 in spaced relationship, the bracket means 15 being attached tothe chuck means 26 by means of screws 27 so as to freely support thesystem 10, 11, 12 by hearing against it at regions opposite to thesupport members 11. Furthermore, the bracket means 15 are provided, onboth their front surfaces,with bracket plates 28 fixed to the formerlikewisely by means of screws 29.

The bracket plates 28 of which, for sake of clarity, only one isillustrated in Fig. 8 are selected so as to protrude behind the frontsurfaces of the die thereby preventing it from being pushed from withinthe chuck means 26 during operation. An adjustable abutment means formedas a screw 31 is arranged on the chuck means 26 in such a manner thatits inward end 32 may abut against one of the girder members 12 of thedie, the function of the abutment means 31, 32 being to limit theelastic deformation of the system 10, 11, 12 to a predetermined value,i. e. 'to fix the maximum value of the clearance angle a when the workpiece 14 is rotated in the direction indicated'by the arrow 30. Such alimiting action may be needed in cases where the material of the workpiece 14 is not quite homogeneous and there are regions in it thehardness of which exceeds the preselected value. When going over tocutting such a region the clearance angle at would be altered and thedie would cut at a less value of its working radius 19 so that thecutting would result in a work piece 14 of a relatively smallerdiameter. In such cases the preselected value of the clearance angle oris maintained by bearing of the abutment means 31, 32 against the outerflank of the girder member associated therewith. The system beinguniformly deformable around the axis 13 of rotation, the rest of themembers 12 will occupy a like position with the same clearance angle a.without the need of applying further abutment means 31, 32 eachassociated with one of the girder members 12. If the cutting edgesstrike upon regions the hardness of which is less than the preselectedvalue, the die is liable to cut threads of an increased diameter.However, the dimensions of the die can obviously be selected so thatdifferences as to the diameter of the thread cut by the die be slightenough to fall within the limits of the standardized tolerances even iffree fit of the threads is required. .The chuck means 26 is, by means oftwo brackets 33, connected to a sleeve 34 adapted to be mounted on thetailstock of a lathe. On the other hand, the work piece 14 is clamped inthe headstock spindle of thexsame lathe. Both the tailstock and theheadstock spindle of a lathe as well as the manner of mounting athreadcutting die therebetween are well known in the art and, therefore,not represented in the drawing.

In operation, the die is accommodated within the chuck means 26 in theabove described mannerandthe screw 31 is adjusted so as to limit themaximum value of the clearance angle a. spindle 35 is caused to rotateand the chuck means 26 is displaced toward the headstock spindle 35'soas to bring the cutting edges 10 and the work piece 14 into machiningengagement. As soon as the cutting edges 10 contact with the work piece14, the system 10, 11, 12 becomes elastically deformed in the abovedescribed manner whereby a clearance angle on automatically appearsbehind the cutting edges 10. If the system 10, 11, 12 tends to becomefurther deformed due to inhomogenities of the material of the work piece14 one of the girder members 12 strikes against the abutment means 31,32 associated therewith whereby the system is rendered sulficientlyrigid so as to be prevented from any further deformation. As the cuttingof threads on the work piece 14 goes on, the chuck means 26 with the dieaccommodated therein is drawn toward the headstock spindle 35 by meansof'the.

the thread-cutting edges 10 and the work piece 14 get disengaged. Thedisengaged die resumes its inoperative position wherein thethread-cutting edges 10 are distant from the work piece 14 so thatneither wearing nor split- Thereafter, the headstock ill ting .off ofthe former can occur when the die is removed from the material justmachined.

' What I claim is: 1. A thread cutting die comprising in combination aplurality of cutting edges lying on the circumference of a circle, aplurality of members for supporting said cutting edges extendingradially of the axis and outwardly of the circumference of said circle,and a plurality of elastically deformable arcuate girder membersinterconnecting adjacent support members at positions on said supportmembers spaced from said cutting edges to form a circuitous body, saidcuttingedges when engaging the material to be machined upon 'rotation ofthe die causing said girder members to deform and the trailing portionof said cutting edges'to be tilted radially away from the material andthe forward portion of said cutting edges to be tilted radially inwardsof the material so as to produce a proper clearance angle on saidcutting edges.

' '2. A thread cutting die comprising in combination a plurality ofcutting edges lying on the circumference of a circle, a plurality ofmembers for supporting said cutting edges extending radially of the axisand outwardly of the circumference of said circle, and a plurality ofelastically'deformable arcuate girder members interconnecting adjacentsupport members at positions on supportrnembers spaced outwardly fromthe circle formed by cutting edges to form a circuitous body, saidcutting edges when engaging the material to be machined upon rotation'of the die causing said girder members to deform and the trailingportion of said cutting edges to be tiltedradially away from thematerial and the forward portion of said cutting edges to be tiltedradially inwards of the material so as to produce a proper clearanceangle n'said cutting edges, said girder members being of a predeterminedthickness to provide a predetermined deformation when said cutting edgesengage the material to produce a predetermined clearance angle.

3. thread cutting die comprising in combination a plurality of cuttingedges lying on the circumference of I a circle, three members forsupporting said cutting edges and extending radially of the axisandoutwardly of the circumference of said circle, and three elasticallydeform able arcuate girder members each arranged between two of saidsupporting members, said girder members being connected to adjacentsupportmembers at positions on said support members spaced outwardlyfrom the circle formed by said cutting edges to form a closed circuitousringshaped body, said cutting edges when engaging the material to bemachined upon rotation of the die causing said girder members to deformand the trailing portion of said cutting edges to be tilted radiallyaway from the material and the forward portion of said cutting edges tobe tilted radially inwards of the material so as to produce apredetermined clearance angle on said cutting edges.

4. A thread cutting die comprising in combination a plurality ofcuttingedges lying on the circumference of a circle, a plurality of members forsupporting said cutting edges extending radially of the axis andoutwardly of the circumference of said circle, anda plurality ofelastically deformable arcuate girder members interconnecting adjacentsupport members at points on said support members spaced outwardly fromsaid cutting edges to form a closed circuitous ring shaped body, saidsupporting members and said girder members being symmetrically arrangedwith respect to and around the axis of said circle, said cutting edgeswhen engaging the material to be machined upon rotation of the diecausing said girder members to uniformly deform around the axis of saidcircle and the trailing portion of said cutting edges to be tiltedradially away from the material and the forward portion of said cuttingedges to be tilted radially inwards of the material so as to produce apredetermined clearance angle on said cutting edges.

5. A thread cutting die comprising in combination a plurality of cuttingedgeslying on the circumference of a circle, a plurality of members forsupporting said cutting edges extending radially of the axis andoutwardly of the circumference of said circle, and a plurality ofelastically deformable arcuate girder members interconnecting adjacentsupport members to form a closed circuitous ring shaped body, saidcutting edges, supporting members and girder members being symmetricallyarranged with respect to the radial center lines extending from the axisof said circle through each of said support members so as to render saidbody deformable in both directions around the axis of said circle, saidcutting edges when engaging the material at points on said supportmembers spaced outwardly from said cutting edges to be machined uponrotation of the die causing the girder members to deform and thetrailing portion of said cutting edges to be tilted radially away fromthe material and the forward portion of said cutting edges to be tiltedradially inwards of the material so as to produce a predeterminedclearance angle on said cutting edges.

6. A thread cutting die comprisingin combination a plurality of cuttingedges lying on the circumference of a circle, a plurality of members forsupporting said cutting edges extending radially of the axis andoutwardly of the circumference of said circle, and a plurality ofelastically deformable arcuate girder members integrally formed with andinterconnecting adjacent support members to form a closed circuitousring forming the body of the die, said girder members being spacedoutwardly from the circle formed by said cutting edges, said cuttingedges when engaging the material to be machined upon rotation of the diecausing said girder members to deform and the trailing portion of saidcutting edges to be tilted radially away from the material and theforward portion of said cutting edges to be tilted radially inwards ofthe material so as to produce a predetermined clearance angle on saidcutting edges, said girder members being of a predetermined thickness toautomatically provide said clearance angle upon engagement of saidcutting edges with the material.

7. A thread cutting die comprising in combination a plurality of bitsforming cutting edges lying on the circumference of a circle, aplurality of members for supporting said bits extending radially of theaxis and outwardly of the circumference of said circle, fastening meansfor securing said bits to said supporting members, and a plurality ofelastically deformable arcuate girder members interconnecting adjacentsupport members at points on said support members spaced outwardly fromthe circle formed by said cutting edges to form a closed circuitous ringshaped body, said cutting edges when engaging the material to bemachined upon rotation of the die causing said girder members to deformand the trailing portion of said cutting edges to be tilted radiallyaway from the material and the forward portion of said cutting edges tobe tilted radially inwards of the material so as to produce apredetermined clearance angle on said cutting edges.

8. A thread cutting die mechanism comprising in combination a pluralityof cutting edges lying on the circumference of'a circle, a plurality ofmembers for supporting said cutting edges extending radially of the axisand outwardly of the circumference of said circle, a plurality ofelastically deformable arcuate girder members interconnecting adjacentsupport members at points on said support members spaced outwardly fromthe circle formed by said cutting edges to form a circuitous body,

saidv cutting edges when engaging the material to be ma'- chined uponrotation of the die causing said girder members to deform and thetrailing'portion of said cutting edges to be tilted radially away fromthe material and the forward portion of said cutting edges to be tiltedradially inwards of the material so as to produce a predeterminedclearance angle on said cutting edges, chuck means surrounding said bodyin spaced relationship, and bracket means attached to said chuck meansand provided to support said body by bearing against it at pointsopposite said supporting members.

9. A thread cutting die mechanism comprising in combination a pluralityof cutting edges lying on the circumference of a circle, a plurality ofmembers for supporting said cutting edges extending radially of the axisand outwardly of the circumference of said circle, a plurality ofelastically deformable arcuate girder members interconnecting adjacentsupport members at points on said support members spaced outwardly fromthe circle formed by said cutting edges to form a-circuitous body, saidcutting edges when engaging the material to be machined upon rotation ofthe die causing said girder members to deform and the trailing portionof said cutting edges to be tilted radially away from the material andthe forward portion of said cutting edges to be tilted radially inwardsof the material so as to produce a predetermined clearance angle on saidcutting edges, chuck means surrounding said body in spaced relationship,bracket means attached to said chuck means and provided to support Cirsaid body by hearing against it at points opposite said supportingmembers and between adjacent girder members.

10. A thread cutting die mechanism comprising in combination a pluralityof cutting edges lying on the circumference of a circle, a plurality ofmembers for supporting said cutting edges extending radially of the axisand outwardly of the circumference of said circle, a plurality ofelastically deformable arcuate girder members interconnectingadjacentsupport members at points on said support members spaced outwardly fromthe circle formed by said cutting edges to form a circuitous body, saidcutting edges when engaging the material to be machined upon rotation ofthe die causing said girder members to deform and the trailing portionof said cutting edges to be tilted radially away from the material andthe forward portion of said cutting edges to be tilted radially inwardsof the material so as to produce a predetermined clearance angle on saidcutting edges, chuck means surrounding said body in spaced relationship,bracket means attached to said chuck means and provided to support saidbody by bearing against it at points opposite said supporting members,and adjustable abutment means provided on said chuck means and adaptedto abut against said girder members to limit elastic deformations ofsaid body to a predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS1,220,460 Rioux Mar. 27, 1917 1,564,591 Lansche Dec. 8, 1925 1,796,925Folman Mar. 17, 1931 1,878,216 Wells Sept. 20, 1932 2,513,864 HaycockJuly 4, 1950 FOREIGN PATENTS 500,955 Germany Oct. 3', 1930 658,578 GreatBritain Oct. 10, 1951

